Process for making light conducting plates

ABSTRACT

A process for producing light-conducting plates which are particularly capable of use at the inlet of gamma cameras, is characterized by the use of transparent rods which are placed one next to the other, while means constituting distance holders which are thicker than the length of the light wave to be transmitted, are placed between the rods. At least one end of the rods is fixed by a casing mass, then it is ground and polished, and then the casting mass as well as the grinding and polishing means are removed.

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{54} PROCESS FOR MAKXNG LIGHT [56] References Cited CONDUCTING WATESUNITED EI'ATES PATENTS [75] Inventors: Lorenz". Ortner, Fraucnaurach;3,344.276 9/1967 Balding 150/80 Kari-Gem? n i l g 2,328,302 8/]943:Simison 51/2123 Conrad, b th fE ;J hi;- 3,193.363 7/]965 241C115 et all56/29t'1 Dierker, Buckenhof n of Germany 3,567,549 3/1971 liofirncisteret 71L 65/4 1 Asilgmcl Siemens Aktlengfisfiusihafi, PrimaryExaminer-Alfred L. Lcavitt f Y Assistant Examinew-E-mnk F risendzl14/101716), Agfll, 0r Fl Fi"?l'RlChLll'dS Geier [2]] Appl. No.: 162318{57] ARS'ERACT A process for producing light-conducting plates whichForeign Appli giign Priorit D t are particularly capable of use at theinlet of gen-mm Aug 27 1970 Germany 2042408 cameras, is characterized bythe use 01' transparent i f rods which are placed one next to the other,while 52 US C! U 156 I54, 52 283 4, means consmuting distance holderswhich are tl'ncKer I 156/182) l56/2g6 than the length of the light waveto be transzmtied. are [51] km Ci {2453 1/00 placed between the reds. Atleast one end of the rods 1581 M of 55111111:111113715571513 15' 292 isfixed by casing 11 1s l5(1,/293;5l/283; 350/96 B; 250/80, 227.

213 VT; 65/4, DIG. 7', 29/423, 424

ished, and then the casting mass as \l'ell as the grinding and polishingmeans are removed.

I 5 Claims, 4 Drawing Figures PATENTEDHUY 12 19m Fig.4

A THRI E PROCESS FOR MAKING LIGHT CONDUCTING PLATES a photocathode,wherein electrons are released by the light. The electrons are thentransmitted as a visible image upon a second light screen at the outletof the image changer after they have been subjected to acceleration,multiplying, etc.

Known light-conducting plates include as a rule rods or fibersconsisting of a transparent core carrying a cover having a lowrefraction index which provides the total reflection at the walls of thecore. These devices are quite suitable for the transmission of opticalimages which are greatly enhanced. However, when gamma ray images arebeing transmitted fine imaging is less important than the transmissionof the greatest possible amount of light.

During the manufacture of light conducting plates consisting oftransparent rods, particularly glass rods, placed freely one next to theother it is difficult, to produce optically perfect surfaces without itbeing neces sary to grind and polish the rods after the construction ofthe plate. However, when the completed devices are ground and polished,grinding and polishing means penetrate between the rods and producedeposits which are very difficult to remove. Means remaining at the rodsproduce a loss of light which is particularly detrimental when the lightplates are used in gamma cameras.

An object of the present invention is the provision of a process formaking light-conducting plates which would avoid the drawbacks ofexistingplates and of their manufacture.

Other objects will become apparent in the course of the followingspecification.

In the attainment of the objectives of the present invention it wasfound desirable to place transparent rods in parallel one next to theother, while means constituting distance holders which are thicker thanthe length of the light wave to be transmitted, are placed between therods. At least one end of the rods is fixed by a castmg mass and is alsoground and polished. Then the casting mass, as well as the grinding andpolishing means are removed.

The casting mass, which can be a wax, protects the side surfaces of therods against the effects of water and P events dirtying by polishingmeans. Furthermore, the casting means make the plate mechanically stablega nst vibrations caused by the grinding and polishing f e s etc. lnaddition, edge cuts etc, at the front surcs of the rods are prevented.To remove the casting i lf fll alter the grinding and polishingprocedure, the lfj l used wax is melted out again and the system is"-h'i or example, in an ultra sound bath. The free between the rodspermit free flow of cleaning "8 means. As means for the removal of wax Wa c arttcularly suitable org solvents Such as enome or mixtures.

: n il. out

puts are produced particularly when apparently this is caused by the iats a:

fact that light rays are also received which fall in only very flatly.These rays are caught along the side walls in the manner of a screwwinder. As compared to rods having a square cross-section, this improveslight output by 30 percent. Thus despite a loss at the light catchingsurface covering of at least 10 percent in case of the thickest possiblepacking, there is still a gain in ray transmission of 20 percent.

The material of the transparent rods can be a plastic as well as glass.when selecting the material care must be specially taken that it has thefollowing properties:

ll Good pure transmission in the spectral range of the detector at thegreatest possible refraction index.

2. Very well reflecting outer surface in case of drawn round rods.

3. Glass should be free from potash to avoid a K-40 ray base.

For this reason flint glass can be used which at the sodium-D-line has arefraction index of 1.62.

By the use of deformable parts, it is possible, for example, in case offiber optics of totally reflectingglass rods with gas covering,particularly air covering, to use rods of the usual manufacture, withouthaving to treat them subsequently. Tolerances in thickness which areunavoidable, are balanced by the deformations of the distance holders.The distance holders which can have the shape ofa wire, can consist ofmetals, such as silver, lead, copper, etc. However, other materials canbe also used which can be shaped by deformation, without going back todeformation zero. A deformation which goes back completely to zero,should be avoided, since then there is the danger of breakage of theglass rods. The thickness of the wire-like distance holders should beabout 0.2 to 0.5 mrn, in order to be adapted to the usual deviations inthe thickness of glass rods having a diameter of about 7 mm.

A light-conducting plate'having the features of the present inventioncan be manufactured by pushing the rods into the meshes of a wire screenand then compressing them. By way of example, for image changers usedfor reproducing gamma ray images, glass rods of optical glass can beused consisting of drawn round rods with naturally blank surfaces, whichare about 15 to mm. long with a 7 mm. diameter and having a tolerance ofplus-minus 0.2 mm. They can be also provided with two copper wire rings.The use of an about 0.35 mm. thick cooper wire suffices to balance theexpected tolerances. To produce the light-conducting plate the glassrods are set together so that the wire rings provide on the one hand thejoining of the rods and, on the other hand, guarantee the maintenance ofan air gap between them which is greater than the length of the lightwave. As above stated, the thickness of the used wire rings depends uponthe diarnctric toierance of the glass rods and the deformation capacityof the wire, with reference to use of limited pressure corresponding tothe strength of used materials particularly glass.

To be able to use with success the light-conducting plate of the presentinvention for image transmitting devices as well, it is important thatother optical elements could be optically coupled to the plate. For thatpurpose generally a medium is used such as, for exnrnplc, an immersionoil, which provided the optical coupling. Oils can. be used only if theycannot penetrate into the light-conducting plate (between 'the glassrods). To avoid the penetration of the coupling medium consisting of animmersion layer of silica oil" vide good attachment of the foils uponthe ends of the light-conducting plate and to create good opticalcontact, a transparent-glue is used which can belong to one of severaloptical products and can be prepared upon the epoxide urea base. Priorto the gluing of the second foil the air gap between the glass rods ispreferably filled with loose layered particles of an artificialmaterial, having a diameter of about 0.2 mm. The diameter of theparticles of the filled in powder or granules is not important, however,it must under all circumstances be large in comparison with thepenetrating length ofthe light waves. Particles of the filling thenabsorb the light bundle which has not been caught by thelight-conducting rods and thus prevent its spreading which can lead to adisturbance in the reproduced images (stray light suppression). It ispossible to additionally prevent the penetration of not absorbed lightrays by blackening the space between the rods upon the light inlet side.This will also prevent the widening of the uncaught light which couldlead to the appearance of disturbing stray light base. The blackeningcan be produced, for example, by coating the foil with a photo-emulsionand by the use of a reverse caustic bleaching process. On the otherhand, the creation of an optical mask is also possible by the usual so-called photo-resisting lacquer technics, for example, with a coloredlacquer.

The invention will appearmore clearly from the following detaileddescription whentaken in connection with the accompanying drawingshowing by wayof example only, preferred embodiments of the inventiveidea.

In the drawing:

FIG. I is a section through an image magnifier provided with alight-conducting plate made in accordance with the present invention.

FIG. 2 is a front view ofa rectangular grid of deformable wire withglass rods inserted into its meshes.

FIG. 3 is a front view of a hexagonal grid with glass rods inserted intoits meshes.

FIG. 4 shows in perspective a cut-out portion of-a light-conductingplate made by pressing together glass rods provided with wire rings, theplate being glued upon each of the two optically effective ends by athin plastic foil and wherein the effects of the light entering betweenthe rods is eliminated.

FIG. I shows a glass casing l of an image magnifier.

A pliotocathode 3 is located behind its front plate 2 and and a'lightlayer 11. The screen 9 is coupled to the image magnifying inlet 2 by alight-conducting plate 12 which consists of individual tight-conductingrods 13 as well as wire grids l4 and i5 located at a distance of 15 mm.from each other, the rods 13 being inserted into the meshes of the wiregrids. I

FIG. 2 is an eniarged separate view of the wire grid 14. It is apparentthat when it is compressed by the steel band 16, the wires 17 and 18which consist of copper and are 0.35 mm. thick, are slightly pressedinto the bearing locations of the rods 13 and thus provide a balance forthickness variations of the rods, as well as a firm hold. Thelight-conductors consist of glass rods which are 7 mm. thick and 15 mm.long. On one side they are adapted to the shape of the inlet window 2and they have common concave outer surfaces on that side. The endsurfaces of the plate 12 are connected with polyvinylchloride foilswhich are 60a thick, the foil 19 being located at the side close to thelight screen and the foil 20 being located at the side of the imagechanger. Furthermore, an immersion layer 2Iconsisting of silica oil andhaving a thickness of 0.8 mm. is located between the foil 20 and theinlet surface of the image magnifier. A similar immersion layer is alsoprovided between the layers 11 and 19 to improve light transmission.

Instead of a layer of oil the layers 11 and 19 can be joined by a puttyof artificial resin.

FIG. 3 shows rods 22 of a different light-conducting plate which arecioser packed in the hexagonal holes of the honeycomb grid 23 in orderto increase the light receiving surfaces. In other respects theconstruction is the same as that shown in FIG. 1.

FIG. 4 shows a plate 24 consisting of glass rods 25 which are providedat a distance of about 15 mm. with wire rings 26 and 27 of silver. Therods 25 are tightly packed, as in the arrangement shown in FIG. 3, sothat the wires 26 and 27 engage each other between the glass rods and sothat a space remains consisting of the thickness of only one wire,amounting to 0.35 mm. Furthermore, foils 28 and 29 which are a thick andconsist of polyethylenterephthalate are glued to the optical endsurfaces of the rods by means of layers 30 and 31 with an opoxide resinglue. Granules 32 of a plastic granulate fill in the spaces between therods 25. Furthermore, at the ray inlet side a part upon the foil 28 isblackened by means of a layer 33 which covers parts located outside ofthe end surfaces of the rods 25. Due to this arrangement light comingfrom a light layer corresponding to that indicated as 11 in FIG. I, orfrom another source, can penetrate only at the ends of the rods 25'andcan be further transmitted without disturbance.

It is apparent that the present invention covers not only the describedplates and methods of making them, but also variations thereof withinthe scope of the appended claims. For example, the ground and polishedends of the rods can be glued upon a solid transparent plate, such as asupporting glass plate, and'then the wires can be removed.

We ciaim:

1. A process for making light-conducting plates particularly suitablefor use in inlets of gamma cameras, said process comprising placing nextto each other a plurality of transparent rods and locating between saidrods distance holders consisting of wires of deformable material havinga thickness greater than the length of the light wave to be transmitted,pressing together said rods and said wires, fixing by a casting mass atleast one end of each of said rods, grinding and polishing said ends,removing said casting mass and the grinding and polishing means, thenapplying a foil to at least one front surface of the producedlight-conducting plate, said foil having a thickness of 20 to 100p andfilling spaces remaining between said rods with particles of agranulate, said particles having a large diameter relatively to thelength of said light wave. r

2. A process in accordance with claim 1, wherein saidrods consist ofglass, have a round cross-section and a thickness ranging from 1 to mm.,preferably 7 mm., 4

and wherein said wires consisting of a deformable 6 metal, such ascopper, and having'a diameter ranging between 0.2 to 0.5 mm.

3. A process in accordance with claim I, wherein said foil is applied atthe light entry side of the lightconducting plate, the processcomprising the further step of blackening said foil at parts locatedopposite the spaces between said rodsv 4. A process in accordance withclaim 1, further comprising gluing said ground and polished ends of therods to a solid transparent plate and then removing said distanceholders.

5. A light-conducting plate made in accordance with the processdescribed in claim 1.

1. A process for making light-conducting plates particularly suitablefor use in inlets of gamma cameras, said process comprising placing nextto each other a plurality of transparent rods and locating between saidrods distance holders consisting of wires of deformable material havinga thickness greater than the length of the light wave to be transmitted,pressing together said rods and said wires, fixing by a casting mass atleast one end of each of said rods, grinding and polishing said ends,removing said casting mass and the grinding and polishing means, thenapplying a foil to at least one front surface of the producedlight-conducting plate, said foil having a thickness of 20 to 100 Mu andfilling spaces remaining between said rods with particles of agranulate, said particles having a large diameter relatively to thelength of said light wave.
 2. A process in accordance with claim 1,wherein said rods consist of glass, have a round cross-section and athickness ranging from 1 to 15 mm., preferably 7 mm., and wherein saidwires consisting of a deformable metal, such as copper, and having adiameter ranging between 0.2 to 0.5 mm.
 3. A process in accordance withclaim 1, wherein said foil iS applied at the light entry side of thelight-conducting plate, the process comprising the further step ofblackening said foil at parts located opposite the spaces between saidrods.
 4. A process in accordance with claim 1, further comprising gluingsaid ground and polished ends of the rods to a solid transparent plateand then removing said distance holders.
 5. A light-conducting platemade in accordance with the process described in claim 1.